The present invention relates generally to field sobriety testing, and more particularly, to an apparatus and method for administering Horizontal and Vertical Gaze Nystagmus tests to enable an officer of the law to make an initial determination as to the possibility of impairment, and for use as evidence in judicial proceedings.
Driving under the influence of alcohol (D.U.I.) and, to a lesser extent, drugs is responsible for approximately one-half of all motor vehicle fatalities annually in the United States. In recent years, tougher enforcement and penalties have been successful in reducing accidents as a result of drunk driving. Typically, drivers suspected of D.U.I. are stopped and given a battery of field sobriety tests. These include Horizontal Gaze Nystagmus (HGN), Walk and Turn (WAT), One Leg Stand (OLS), Finger-to-Nose (FTN), and Romberg combined with Alphabet Recitation. These are typically administered by the officer to establish probable cause to arrest the suspect on suspicion of DUI. More conclusive evidence of impairment is then established or bolstered through breathalizer and/or blood testing.
"Nystagmus" is defined as an involuntary jerking of the eyeballs. Horizontal Gaze Nystagmus refers to an involuntary jerking of the eyes occurring as the eyes gaze to one side, usually at the point of maximum pupillary deviation. This phenomenon is involuntary and unconscious. The test subject exhibiting the nystagmus is normally unaware of such jerking, and is unable to stop it. When under the influence of alcohol and/or drugs, the jerking of the eyeballs becomes exacerbated and is readily noticeable. Higher concentrations of alcohol and/or drugs result in rapid jerking movement as soon as the pupil moves to the side. Studies have shown that the Horizontal Gaze Nystagmus is the most accurate of the field sobriety tests.
In a typical Horizontal Gaze Nystagmus test, the officer holds an elongated target object such as a pen, pencil or penlight, at a distance of approximately twelve (12) to fifteen (15) inches in front of the suspect. The test subject is then instructed to focus on and track the target as the officer moves it from side to side. An impaired test subject cannot smoothly follow a slow moving object. The average eye tracks approximately 20 degrees per second. When intoxicated, the eyeballs can easily be observed to jerk or bounce as they move horizontally left and right. When the pupil of the eyeball moves to a location of maximum pupillary deviation (the 45 degree position), distinct and aggravated jerking are manifested. Although many people exhibit slight jerking tendencies even when sober, the jerking becomes very pronounced and readily observable when under the influence. The greater the degree of impairment, the sooner the jerking begins. A blood alcohol content (BAC) of 0.10% or more (the legal limit in most states) will likely cause pronounced eyeball jerking well before the eyeball moves to the 45 degree position.
Vertical Gaze Nystagmus testing is used to reveal the possible presence of PCP as well as central nervous system depressants such as alcohol or inhalants. It is most apparent when the test subject has taken high doses of CNS depressants or inhalants. The VGN test is administered in a manner similar to the HGN test, except that in the former the target is moved in a vertical orientation from an initial point at approximately eye of nose level, and the suspect is instructed to track the target until the pupil reaches the 45 degree position.
Recent legal trends have classified field sobriety tests as "testimonial" in nature, i.e., they are subject to the same admissibility conditions and constitutional safeguards as other kinds of testimony in criminal proceedings. Because of these rulings, the Romberg and counting portion of other exercises have been ruled inadmissible unless Miranda warnings were previously read to the suspect. In spite of the fact that HGN has been shown to be a scientifically reliable indicator of alcohol or drug impairment, HGN is often challenged by defense counsel as being unreliable due to the inconsistent administration of the test by police officers in the field. Because the officer performs the test by positioning and then moving the target in front of the test subject without any physical way to control test parameters such as distance and range of motion, the legal attack in court is founded on the premise that since these tests are not uniformly administered, i.e., no control on the foregoing parameters, they are consequently unreliable and therefore should be inadmissable.